South African spinner Johan Botha, reported for a suspected illegal bowling action, will sit out his team's final one-day international against Australia at the Wanderers Stadium Friday.

Captain Graeme Smith admitted: "We've decided not to play Johan, just to take the focus off him."

South Africa have a winning 3-1 lead in the five-match series.

Botha was reported by umpires Brian Jerling, Asoka de Silva and television umpire Rudi Koertzen after the fourth match in Port Elizabeth Monday.

The off-spinner has been a key figure in two successive South African one-day series wins over Australia.

He led the team in a series in Australia earlier in the season when Smith was injured. In both series his economical bowling and an ability to take top-order wickets prevented the Australian batsmen from achieving big totals.

Coach Mickey Arthur and bowling coach Vincent Barnes have come to the defence of Botha, who is seen as playing a key role for South Africa in the T20 WC in England in June.

Although the umpires cast suspicion on Botha's faster ball and his doosra - the off-spinner's googly - Barnes said none of the 18 video clips supplied by the International Cricket Council showed Botha bowling a doosra.

Barnes is confident that Botha's action will pass scrutiny following remedial work done by the bowler after he was banned from bowling in international cricket in 2006 because his "elbow flexion" exceeded the maximum permitted 15 degrees.

Botha is expected to fly to Perth soon for testing at the University of Western Australia where he was passed for bowling again after his first ban.